Thermal vaporizers, such as electric mosquito controlling devices, include those of the mat type wherein a mat impregnated with an insecticidal solution is used as placed on a heat plate, and those of the liquid type wherein a chemical solution is heated for vaporization while being drawn up through a wick from a bottle. Those of the mat type include cordless devices already proposed, while cordless devices of the liquid type have yet to be proposed. The electric mosquito controlling device of the liquid type is relatively heavy in its entirety since the overall weight of the device includes the weight of the device body and that of the solution bottle. If cordless, the entire device must be supported against gravity solely by a plug attached to the electric outlet. It is therefore likely that the plug will slip off the outlet when the device is heavy. This defect has been a serious obstacle to overcome in designing cordless liquid-type devices. For example, the conventional electric mosquito controlling device of the liquid type with a cord comprises a box-shaped body and is used with a solution bottle accommodated in the body. The device body of the conventional structure must have a height at least sufficient for the body to accommodate the solution bottle and the wick projecting upward from the bottle, and is consequently large-sized, heavy and unsuited for use as a cordless device. The device is further inconvenient in that the bottom portion of the device body needs to be removed when the solution bottle is to be accommodated in the body.